very confused

okay guyssss. long post i’m sorry. okay we have been trying for almost four years with only two positives to show for. last august being the first positive we got we knew for a week and then i had a miscarriage (when tested my levels of hcg was 218) i’m #rhnegative so they suspected that being the cause of miscarriage they gave me the shot in my arm (from last known af to miscarriage it was 5 weeks 5 days). fast forward to may 29 this year was my last af i missed june and got a positive july 8. however three days later i miscarried (my levels of hcg was 18). they gave me the shot in my hip this time. i miscarried for about a week of “af” i kept getting on and off positive/ negative tests so i just ended up not taking anymore. it’s now august so i’m past the 5 weeks 5 days (i’m late) if i based it off of last time i miscarried how am i late when i had “less” hcg in my body. i’m so scared to test and lose another baby. has this happened to anyone else?